Biogas Upgrading by Capturing CO₂ in Non-aqueous Phase-Changing Diamine Solutions

Abstract

Ethanol solutions of diamine, ethylenediamine (EDA) or piperazine (PZ), were found to be able to produce a solid precipitate after the absorption of CO2. The precipitate was identified to be a mixture of monocarbamate and dicarbamate. The details of the reactions between CO2 and diamine were examined. Results show that EDA–ethanol solutions exhibit higher capacity and faster rate for CO2 absorption than PZ–ethanol solutions. As a comparison, the kinetics of CO2 absorption with diamine–water solutions were also tested. It was found that the overall average absorption rate of CO2 in EDA–ethanol solutions is almost double that in EDA–water solutions. Moreover, results show that EDA–carbamate has a decomposition temperature of ∼90 °C and requires a regeneration energy of 25.6% less than traditional monoethanolamine (MEA) solutions, which suggests that EDA–ethanol solutions are promising to be used as cost-effective absorbents for CO2 capture.